The invention relates to endless power transmission belts, but more particularly, the invention relates to generally flat belts having a plurality of circumferential ribs adapted to engage a multi-grooved pulley.
Originally, multi-ribbed belts and pulleys were as disclosed in U.S. Pat. No. 2,728,239. Ribs of such belts were configured to register in pulley grooves to make complete contact with the walls of the pulley so that there was no clearance space between the belt ribs and pulley grooves during operation of the belt with the pulley. It was reasoned that the zero clearance permitted the belt ribs to set up a hydrostatic pressure from radial thrust urging the belt toward the pulley during its passage around the pulley.
The requirement for zero clearance between belt ribs and pulley grooves has eroded over the past twenty-five years as ribbed belts have been further developed for improved power transmission. The trend has been to provide clearance between a belt rib and pulley groove by making the belt rib smaller than the pulley groove to provide a radial clearance when viewed in cross section. Examples of such radial clearance appear in U.S. Pat. Nos. 3,643,518 and 4,047,446. A radial groove between adjacent belt ribs provides a positive clearance between the belt and the apexes of a grooved pulley in U.S. Pat. Nos. 3,818,741 and 4,047,446 to allow for wear of the belt ribs while preventing projections of the pulley between pulley grooves from contacting the belt. Such clearances prolong belt life.
In the known multi-ribbed belt and grooved pulley power transmission systems, the belt ribs have an angle that is substantially equal to or greater than the groove angle in the grooved pulley. While such clearance arrangements may provide improved performance of multi-rib belts, such clearances are not effective in alleviating manufacturing tolerances associated with belt rib and pulley groove spacing and contour for the purpose of improving belt fit. It is believed that a good fit between a multiple rib belt and its grooved pulley enhances belt life by providing better distribution of frictional loads between the belt ribs and pulley. The problem has been to get the good belt/pulley fit during early, and preferably all, stages of belt operation.